Add copyright watermark to PDF in Swift for iOS

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//
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//  Copyright © 2019-2026 PSPDFKit GmbH. All rights reserved.
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//
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//  The Nutrient sample applications are licensed with a modified BSD license.
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//  Please see License for details. This notice may not be removed from this file.
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//
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import PSPDFKit
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import PSPDFKitUI
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private let copyrightNotice = "Copyright 2019 ACMe Corp."
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private class WatermarkingSharingViewController: PDFDocumentSharingViewController {
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    enum WatermarkPosition {
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        case none
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        case cover
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        case bottomLeft
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        case bottomRight
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        var textAttributes: [NSAttributedString.Key: Any] {
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            switch self {
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            case .none: return [:]
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            case .cover:
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                return [NSAttributedString.Key.font: UIFont.boldSystemFont(ofSize: 100), NSAttributedString.Key.foregroundColor: UIColor.red]
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            case .bottomLeft:
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                return [NSAttributedString.Key.font: UIFont.systemFont(ofSize: 20), NSAttributedString.Key.foregroundColor: UIColor.red]
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            case .bottomRight:
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                var rightAttributes = WatermarkPosition.bottomLeft.textAttributes
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                let paragraphStyle = NSMutableParagraphStyle()
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                paragraphStyle.alignment = .right
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                rightAttributes[NSAttributedString.Key.paragraphStyle] = paragraphStyle
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                return rightAttributes
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            }
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        }
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        func updateContext(_ context: CGContext, rect: CGRect) {
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            switch self {
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            case .none: break
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            case .cover:
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                context.translateBy(x: 0, y: rect.size.height / 2)
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                context.rotate(by: -CGFloat.pi / 4)
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            case .bottomLeft, .bottomRight:
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                // Calculate the Y margin.
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                let usedFont = textAttributes[NSAttributedString.Key.font] as? UIFont
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                let fontSize = usedFont?.pointSize ?? 20
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                let xMargin: CGFloat = self == .bottomLeft ? 10 : -10
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                context.translateBy(x: xMargin, y: rect.size.height - fontSize * 1.5)
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            }
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        }
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    }
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    var watermarkPosition: WatermarkPosition = .cover
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    override func configureProcessorConfigurationOptions(_ processorConfiguration: Processor.Configuration) {
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        // Get a copy here to avoid capturing self in the block below.
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        let position = watermarkPosition
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        // Avoid messing with the processor configuration if we shouldn't be adding a watermark at all.
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        guard position != .none else {
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            return
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        }
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        // This configuration is going to be applied to all of the pages that the user selected
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        // in the sharing UI. Please note that the pageIndex parameter here is based on the pages
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        // being shared, not the source document. So if the user shares pages 5 through 10, the
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        // first call to this closure will have pageIndex = 0, the second one pageIndex = 1, and so on.
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        //
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        // This closure is executed on background threads. Make sure to only use thread-safe drawing methods.
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        processorConfiguration.drawOnAllCurrentPages { context, _, cropBox, _ in
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            let drawingContext = NSStringDrawingContext()
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            drawingContext.minimumScaleFactor = 0.1
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            // Update the context to our desired position configuration
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            position.updateContext(context, rect: cropBox)
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            (copyrightNotice as NSString).draw(with: cropBox, options: NSStringDrawingOptions.usesLineFragmentOrigin, attributes: position.textAttributes, context: drawingContext)
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        }
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    }
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}
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class CopyrightSharedContentExample: Example, PDFViewControllerDelegate {
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    override init() {
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        super.init()
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        title = "Add Copyright to Shared Content"
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        contentDescription = "Shows different ways to add copyright notices to shared contents."
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        category = .sharing
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        priority = 900
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController? {
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        let document = AssetLoader.document(for: .welcome)
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        let pdfController = PDFViewController(document: document, delegate: self) {
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            // Register our watermarking subclass to be used instead of the default class.
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            $0.overrideClass(PDFDocumentSharingViewController.self, with: WatermarkingSharingViewController.self)
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            let sharingConfiguration = DocumentSharingConfiguration {
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                // Remove the ability to share as images.
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                $0.fileFormatOptions.remove(.image)
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                // Remove the Summary annotation option.
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                $0.annotationOptions.remove(.summary)
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            }
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            $0.sharingConfigurations = [sharingConfiguration]
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        }
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        return pdfController
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    }
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    // MARK: - PDFViewControllerDelegate
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    func pdfViewController(_ pdfController: PDFViewController, shouldShow controller: UIViewController, options: [String: Any]? = nil, animated: Bool) -> Bool {
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        guard let watermarkingSharingController = controller as? WatermarkingSharingViewController else {
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            return true
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        }
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        // Hook to change the position of the watermark based on some extra logic.
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        watermarkingSharingController.watermarkPosition = .cover
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        return true
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    }
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    func pdfViewController(_ sender: PDFViewController, menuForText glyphs: GlyphSequence, onPageView pageView: PDFPageView, appearance: EditMenuAppearance, suggestedMenu: UIMenu) -> UIMenu {
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        // Modify the selected text to add our copyright information.
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        let copyrightedText = [glyphs.text, copyrightNotice].joined(separator: "\n")
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        // Create custom actions for copying and sharing.
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        let copyAction = UIAction(title: "Copy", image: UIImage(systemName: "doc.on.doc")) { _ in
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            UIPasteboard.general.string = copyrightedText
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        }
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        let shareAction = UIAction(title: "Share…", image: UIImage(systemName: "square.and.arrow.up")) { _ in
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            let activityViewController = UIActivityViewController(activityItems: [copyrightedText], applicationActivities: nil)
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            let sourceRect = sender.view.convert(glyphs.boundingBox, from: pageView.pdfCoordinateSpace)
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            sender.present(activityViewController, options: [.sourceRect: sourceRect], animated: true, sender: nil)
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        }
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        // Replace the Copy and Share actions with our own.
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        return suggestedMenu
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            .replace(action: .PSPDFKit.copy, with: copyAction)
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            .replace(action: .PSPDFKit.share, with: shareAction)
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    }
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}